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THE SOUND OF SILENCE The M&E contractor’s essential guide to acoustic drainage

THE SOund Of SilEncE - Rehau...represent absolute silence but describes in fact a sound pressure level SPL of 20µPa. The most common mistake is to assume that 10 decibels SPL are

Apr 24, 2020



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  • THE SOund Of SilEncEThe M&E contractor’s essential guide to acoustic drainage

  • fOREWORd:The big noise in internal drainage

    In London, for example, there are now 3,900 residents per square mile, often living in high rise apartments and flats that are expensive to purchase.

    All of this creates a much greater expectation on the performance of the building. If you’ve paid the average London apartment cost of £556,146, you rightly expect to be living in a property free from the sound of running water when the occupants of the flat upstairs take a shower or flush the toilet. And it’s not just the multi-residential sector. Hospitals, libraries and offices all need to mitigate the sound effects of internal drainage to create environments that aid recovery, study and work.

    As a result, the importance of acoustic drainage is elevated. And yet, many contractors remain in the dark about the true causes of internal noise, confused by the terminology and unaware of the different options that are available to mitigate its affects.

    Good internal drainage can help provide a comfortable working or living environment. Poor internal drainage or poor installation can ruin building performance and be a major issue for tenants and owners.

    The truth is that small changes to the specification of drainage can make a huge difference when it comes to mitigating noise levels within a building and a number of important considerations need to be factored in at the outset.

    This guide aims to provide a comprehensive guide through the internal drainage maze that so many contractors find themselves trapped in. Our aim is to answer the many questions that surround the specification and use of internal drainage, slay some myths and guide its proper use and specification.

    Thank you for reading.

    Modern buildings are very different from their counterparts of decades ago. With space at a premium in urban areas, buildings are being constructed upwards, rather than outwards and people live, work and play in much closer proximity.

    Franz HuelleHead of Technical - Building SolutionsREHAU UK Ltd


  • THESE WallS aRE papER THin

    For homeowners or tenants, noise pollution, from either internal or external sources, is their greatest concern.

    The graph below, illustrates homeowner research about the biggest annoyances they find in their homes.

    Whilst neighbourhood conflicts, parking and boring house design are all significant factors for homeowners, along with weak infrastructure, noise

    pollution, cited by 54 per cent of respondents is the biggest concern.

    Why? The reasons will differ from individual to individual, but my own experience suggests that noise pollution is a major contributor to disturbed sleep. In fact, World Health Organisation research suggest one in five Europeans are regularly exposed to sound levels at night that could significantly damage their health, with effects including psychosis and mental health issues.

    Source: Informationszentrum Beton aus RAS 4/94

    What negative facts do house owners mention concerning housing?

    0% 10% 20% 30% 40% 50% 60%

    Noise pollution

    Boring house design

    Lack of parking spaces

    Conflicts in the neighbourhood

    Weak infrastructure

    Lack of childrens play areas

    Distance from work








    How many times have you been in a public building, such as a library or a hospital and heard someone complain about ‘paper thin walls’ as water rushes through the pipework.


  • The decibel scale is very different from standard scales because the human ear is extraordinarily sensitive. It is able to pick up everything from the rustling of tissue paper through to the roar of a Formula One car.

    A logarithmic scale allows engineers to work with more sensible numbers within this enormous range of sound pressures. Very importantly it is a ratio of the measured sound pressure to a reference sound pressure, the hearing threshold of a healthy human ear. So a 0dB sound pressure level (SPL) does not represent absolute silence but describes in fact a sound pressure level SPL of 20µPa.

    The most common mistake is to assume that 10 decibels SPL are twice as loud as 5. Below 40dB SPL, a 3dB increase can generally already be perceived by many as a doubling in loudness. However it must be pointed out that because our ears have different sensitivity across the various frequencies of our hearing spectrum, perceived loudness is very subjective and what is loud to one person may be acceptable to the other.

    undERSTanding dEcibElS

    Before we look at the causes of noise pollution and investigate some potential solutions, it is important to understand how sound levels are measured. Decibels, or dB, work differently to other scales and this often creates significant confusion.

    Sound Pressure Levels


    0 dB

    40 dB

    80 dB

    120 dB

    100 dB

    140 dB

    60 dB

    20 dB

    Threshold of audibility

    Threshold of pain

    Sleeping room ambience

    Start of a jet

    Rock concert

    Jack Hammer

    Ordinary Traffic




    Sound pressure levels (SPL)

  • WHy dO acOuSTicS nEEd TO bE ManagEd?

    It is therefore vitally important during construction to ensure that both noise and vibration are controlled, because finding and locating the source of the problem afterwards can be a difficult, time-intensive, and costly process.

    Part E of the English & Welsh Building Regulations, which specifically deals with passage of sound in buildings, compounds the problem. Whereas in other countries, Building Regulations specify that a building’s technical services must not exceed an absolute dB level, the UK’s simply states a minimum airborne sound reduction target for the noise transfer from one room to another. This means consultants need to habitually specify above the UK regulatory standard to ensure a comfortable environment for occupants.

    Specifically Part E mandates that sound transfer from one flat to another must be reduced by at least 43-45 dB through the partitioning wall or floor.

    Noise is transmitted through both the air and the building structure itself. In fact, vibrations move quicker through the structure of the building than through the air.


    However, Part E does not address the issue of building service noise at all. Although any residential building constructed in England & Wales has to have the capability to reduce airborne noise by circa 43-45dB, the verification on site is carried out without any water flowing through pipes or building services running.

    The problems start once the building is occupied and the building services become operational. At this point noise levels are often found to be significantly different.

    In my experience this is an on-going problem in lower-specification developments, such as student halls of residence, because expert knowledge of the acoustic issue is missing at build stage.

    High-end developments, such as West End Central London luxury apartments, will often have an acoustic consultant assigned to the development, who will specify pipework and infrastructure that will usually go above and beyond the regulations.

    Standard HT-PP pipe showing high noise level using an acoustic camera

  • All-too-often, the consultant specifies an acoustic soil waste system. This, in turn, gets handed down to the M&E contractor who approaches the acoustic drainage manufacturer or merchant who provides a quote for acoustic pipe and components.

    The M&E contractor then goes to the builder’s merchant and finds that the merchant has the pipe but not the complimentary bracketry. Instead the contractor, understandably because he or she is working to tight deadlines, decides to use a generic bracket.

    “It won’t do any harm will it? A bracket’s a bracket and what’s more we’ll save money too”, goes the theory. In a ten-story building the contractor may save £8 per bracket, which equates to around £1800 for the entire system, depending on the number of stacks.

    However, innocent decisions have consequences, due to the fact that the generic bracket compromises the acoustic performance of the system, because the bracket plays a major role in the separation of the vibrations from the wall.

    With acoustic drainage, if you mix and match it has a dramatic effect on acoustic performance and it is therefore crucial to use all the system components and install them in the right way.

    The moral of the story? Acoustic drainage is much more than acoustic pipes. It’s bracketry and fittings too.

    THE big MiSTakE

    The big mistake we find being made over and over again is the incorrect matching of pipe to bracketry. Let me explain.


    RAUPIANO Plus soil & waste installation in apartments, Financial Centre, Istanabul

  • METHOdS Of nOiSE REducTiOn

    1. Cavity absorptions

    Cavity absorption involves the use of a duct wall lined with a sound absorbing material. The problem with this method is that it can take up valuable square footage space, which cannot be either utilised or rented and that the better absorbing linings typically require a more extensive elaborate fixing method.

    There are three methods of insulating against airborne noise

    220 kg/m²

    2. aCoustiC pipe wrap

    There are various types of acoustic pipe wraps available which attempt to absorb sound. Typically, they use laminated products reinforced with aluminium foil, or in its simplest form, un-faced mineral wool. The material is wrapped around ductwork, rainwater, soil & vent or service pipe and then covered with an aluminium foil.

    3. aCoustiC pipe

    Acoustic pipe uses a different method. Rather than trying to absorb sound the pipe is designed to minimise the creation of noise and the transfer of vibrations into the building structure. Typical acoustic pipe uses a multi-layer pipe construction that increases the pipe rigidity and enhances the acoustic properties.


    Example of cavity absorption

    Example of pipe lagging

    Example of acoustic pipe

  • pipe and fitting weight

    Noise is created when water etc impacts on the pipe work, particularly where the system has sharp bends. The acoustic performance of a drainage pipe system can be tweaked through the weight of the pipe and fittings, with heavier pipe less susceptible to water-initiated vibration. For example, cast iron is a very heavy material that is extremely efficient at dampening vibration.

    Why therefore do we not just specify cast iron pipework on every job? Well, obviously cost is a major consideration, but the weight of cast iron requires very sturdy bracketry. Also, the ease of handling heavy materials onsite also needs to be taken into consideration.

    MiniMiSing VibRaTiOn

    We have already touched upon the inherent link between vibration and noise. Vibration therefore needs to be minimised by:

    Another challenge is to reduce the transfer of vibrations into the building wall as much as possible in order to minimise the propagation of structure borne noise within the building.

    There are a number of considerations. Firstly, it is important to avoid direct contact between the pipe and building structure, with a common problem being the failure to separate the stack sufficiently from the building fabric.

    A particular focus should be fire stop collars and other services. Standard fire collars create a sound bridge between the pipe, fire collar and the building fabric. It is therefore important to specify and fit fire collars that have an extra piece that creates sound dampening effects between the pipe and the fire collar. The cost differential is approximately £10 which extrapolates to circa £1,000 for an entire building. A not insignificant cost, but the downside if not fitted is that the acoustics for the entire building are compromised.

    The second issue is to minimise any leftover vibrations through the pipe brackets, as the wall magnifies vibration and then accelerates them through the building at a much faster rate than through the air.

    The third issue is the direction of the water flow. Water creates maximum noise in the pipework when it comes up against sharp bends. Pipe system design must therefore ideally avoid sharp changes of direction as much as possible.

    However, in a practical sense there will always be situations in which pipework has to be fitted into confined spaces. In these situations, it is important that the elbows and branch fittings are capable of minimising vibration as much as possible.


    MiniMising struCture-borne noise transfer

  • a WORd On labORaTORy TESTing

    While standardised laboratory tests of an installed stack are widely advertised and used in the industry, they were only ever meant to allow an acoustic comparison of different systems and do not represent the actual acoustic performance of a system in a real building.

    To get a more realistic grasp on acoustic performance many manufacturers have gone down the route of testing mock-ups. At REHAU, for example, we will install a full bathroom and then perform various tests, such as flushing toilets for example, in order that we can take an acoustic measurement. This is a much more transferable reading than the aforementioned simple test of a single soil and waste stack.

    Many contractors will, understandably, place a lot of emphasis on laboratory testing when selecting acoustic drainage products.


    Example of a mock-up test

  • The RAUPIANO PLUS multi-layer pipe construction achieves superior performance through the application of distinct functional layers. Combined in a composite construction, three separate layers impart unique characteristics to the pipe:

    1. The abrasion resistant, low-friction inner layer ensures the easy transit of waste.

    2. The mineral filled mid-layer ensures superb sound dampening properties and offers increased stiffness.

    3. The robust outer layer is tough enough to withstand impacts and shocks.

    Combined together, the composite layers create a tough, durable pipe, with outstanding acoustic properties that offer all the functionality of a drainage pipe system combined with the noise insulating properties of lagging.

    RAUPIANO PLUS Fittings

    The pipe system can experience local vibrations and redirections, which can have a negative effect on sound performance. RAUPIANO PLUS fittings are specifically designed for sound critical areas, such as elbows, stabilising the sound behaviour, reducing sound generation and achieving best-in-class noise dampening in the impact area.

    RaupianO pluS

    The RAUPIANO PLUS polypropylene-based soil and waste system is suitable in a wide range of buildings from comfortable homes, modern hospitals, and hectic commercial kitchens to contemporary skyscrapers. It is a multi-layer pipe construction which helps to increase pipe rigidity and enhance the sound insulation properties. The smooth, abrasion-resistant inner layer optimises the flow, whilst the impact-resistant outer layer provides robustness for handling on construction sites.


    1. RAUPIANO Acoustic Soil & waste pipe2. RAUPIANO angled fireproofing mounting collar3. RAUPIANO fire protection tape4. RAUPIANO Fireproofing collar compact





  • REHAU Ltd Hill Court, Walford, Ross-on-Wye, Herefordshire, HR9 5QN

    October 2018

    cOncluSiOn:prevention is better than cure

    For too long, the default mindset has been that contractors are happy to cure the problem by wrapping the pipes in mineral wool or foam acoustic wrap, rather than prevent the generation of sound in the first place.

    This mindset needs to change through paying closer attention to the following:

    • Pipe&fittingweight

    • Bracketing

    • Waterflow

    • Avoidinganydirectcontactofpipewithbuilding structure or other services

    Only at that point, can the contractor, the developer and, perhaps most importantly, the tenant or homeowner, have full confidence in the ability of the property to minimise noise from drainage systems which should be “out of sight, out of mind”.

    As interest and awareness of noise levels in our buildings continues to grow, it is vital that effective acoustic drainage becomes part of the M&E Contractor’s toolkit.



    REHAU Building Solutions

    cOnTacT REHau